JP2014-68490A discloses a fuel cell system having fuel cells connected to a power supply line that connects a vehicle battery and a motor to each other. In addition, JP2014-68490A proposes using solid oxide fuel cells having conversion efficiency higher than that of conventional solid polymer fuel cells as vehicle-mounted fuel cells. However, in order to stop this fuel cell system, it is necessary to lower a fuel cell output voltage (open circuit voltage) to a voltage safe to touch a human body (target voltage). For this reason, in the related art, a discharge circuit is installed in the fuel cell, and supply of a cathode gas is stopped in the event of a system stop, so that the open circuit voltage is forcibly lowered by driving the discharge circuit.